How To Replace State Select Heater Thermocouple [3 Easy Steps]

If your pilot light goes out, one of the most common culprits behind it is a faulty thermocouple. As it’s easy to replace on your own, you shouldn’t waste your money hiring a plumber to do it. So, how to replace State Select water heater thermocouple?

The process of doing it varies a little bit depending on the type of gas valve your heater has. However, the underlying idea is the same – you take out the thermocouple from the heater, replace it with a new one, and put it back.

Lucky for you, I’ll be addressing how you can replace the thermocouple for both common types of gas valves. Keep on reading to find out all about it. So, let’s dive in!

How To Replace State Select Heater Thermocouple [Older Gas Valves]

If you have an older State Select heater, then you most likely have a gas valve that looks like this:

state select watert heater old gas valve

These types of gas control valves are really common. Models like State Select GS650YBRT have such valves. Replacing the thermocouple on these types of models is slightly easier than the newer ones.

Before we dive deep into how you can replace it, you need to be sure that the thermocouple is faulty. Thankfully, you can easily test it out with a multimeter. Follow these steps to do it:

  • Remove the end of the thermocouple that’s connected to the gas control valve with an adjustable wrench.
  • Set the multimeter to DC volts and the range should be at millivolts.
  • Connect the red probe of the multimeter with the copper part of the thermocouple and the black probe to the silver knob.
  • Now, attempt to light the pilot by holding down the knob and pressing the igniter. The voltage of the thermocouple should start going up as it’ll start to detect the heat from the pilot light.
  • Collect the readings after following this procedure for one minute.
state select water heater thermocouple testing

If you get a reading above 20 millivolts, it indicates that the thermocouple is fine and it’s not the main culprit here. However, if the reading is below it, you can be sure that something is wrong with your thermocouple.

Now, if the test reveals that you have a bad thermocouple, here’s how you can go about replacing it:

Step 01 – Remove The Necessary Gas Valve Connections

Shut off the main gas supply to the heater by closing the valve. Turn the thermostat to the “Off” position. Give the heater some time to cool down.

Remove the thermocouple, pilot tube, and the main burner gas supply line from the gas control valve.

Here are the wrench sizes you’ll need to remove each of the connections:

wrench sizes to remove the gas valve connections

Remember to use a wrench of the right size when you do this job. If you use the wrong wrench, you can damage the components and break them. Also, make sure that you don’t bend any of the pipes when you take them out. It’ll lead to a more expensive repair job if you do that.

Step 02 – Take The Burner Assembly Out

Remove the manifold cover that gives you access to the viewport. Disconnect the wires connected to the thermal switch. Unscrew the two ¼” bolts holding the manifold door in place and pull the door out. Slide the main burner assembly out of the heater.

state select water heater pulling out burner assembly

Step 03 – Replace The Thermocouple

Remove the screws that hold the thermocouple in its place. Take out the rubber piece located on the manifold door using a flat-blade screwdriver.

Then, you can slide the thermocouple assembly out through the gap in the manifold door. Put the new thermocouple in place of the old one, put it through the manifold door, and connect it to the main burner. Once you do that, reverse engineer the above steps to complete the installation.

So, that’s how you can replace the thermocouple on the older gas valve models. Remember that you won’t always have to replace the thermocouple. Sometimes, they’ll just be dirty, and cleaning the thermocouple with fine-grit sandpaper will do the trick.

They can also be bent out of shape. In that case, readjusting the thermocouple to the right position will solve the issue. However, the most effective long-term solution is to replace it.

State Select Water Heater Thermocouple Replacement [Newer Gas Valves]

In the newer gas control valves, the flame sensor is embedded within the pilot light assembly. The main process of replacing the thermopile or thermocouple or flamer sensor is fundamentally the same on these valves as well.

But it varies a little bit as the components are connected a little differently. Here’s how these gas control valves with a status light look:

state select water heater newer gas valve

Before we get into how to replace the thermopile on these models, you need to know if your thermopile is actually bad. Just like the last one, you can test it with a multimeter. Here’s how to do it:

  • Set the multimeter to Volts DC option.
  • Disconnect the two wires that lead to the gas control valve.
  • Connect the two probes of the multimeter to the two connectors.
  • Relight the pilot light and check how much the voltage increases as the flame sensor starts to heat up.
state select water heater thermocouple testing with a multimeter

You should get a reading between 650-850 millivolts if you have a healthy flame sensor. If you get a reading outside that range, that means you have a faulty flame sensor.

Now, it can be either dirty or damaged and both things will cause a low voltage reading. You need to decide whether you want to clean or replace it. Here’s how you can do both of these things:

Step 01 – Turn Off The Heater

Turn off the gas supply to the water heater. Set the thermostat knob to the “Off” position. Wait for a while for the heater to cool down if you just turned it on.

Step 02 – Pull Out The Main Burner Assembly

Disconnect the igniter wire and the other wires that lead to the control valve.

Remove the wires connected to the thermal switch. Take off the screws holding the viewport door in place. Use an adjustable wrench to loosen the pilot tube and remove it.

state select water heater removing the gas valve connections

Unscrew the manifold tube and take it off. Everything is disconnected at this stage and you should be able to slide the main burner assembly out.

Step 03 – Get The Flame Sensor Out

Use a flat-blade screwdriver to loosen the retaining clip and take it out. Remove the component block that holds the wire in place. Disconnect the screw holding the shield and the pilot assembly to the burner.

state select water heater unscrewing the flame sensor

Feed the pilot tube and wires through the manifold door. Loosen the clip that holds the thermopile in place. Pull out the thermopile.

Step 04 – Clean Or Replace The Flame Sensor

At this stage, you clean the thermopile with an emery cloth and see if that solves the issue. You’d have to reassemble and test it once again. If you don’t want to do all that work, you can just install a new thermopile.

Insert the new thermopile into the pilot light assembly and wiggle it to push it all the way in. Push down the clip and reverse-engineer the above steps to put the pilot assembly back together and insert it into your heater.

When you reinstall the manifold door, make sure the gasket behind it is in good condition. If it’s cracked, you’d have to replace it. Here’s a picture of it:

state select water heater manifold gasket

Your replacement job will be complete once you reassemble the heater with the new thermopile. 


Should I clean anything else when replacing the thermocouple?

Yes, when you take the thermocouple out, it’s a good opportunity to clean the main burner as well as the combustion chamber. Don’t miss out on that and do a thorough cleaning of them to make your heater last longer.

How does the thermocouple in a State Select heater work?

The thermocouple sends a small amount of voltage when it senses that the pilot flame is on. The heater gets the signal that everything is okay and then, it fires up the main burner.

Can a bad thermocouple cause no pilot light?

Yes, when the thermocouple is unable to sense the flame from the pilot light, the main burner doesn’t come on. Hence, the pilot light keeps going out and does not stay lit. Consequently, you don’t get any hot water from your State Select gas water heater.

How long do State Select water heaters last on average?

How long any heater lasts depends on how well you care for them. But if you take good care of your State Select water heater along with proper maintenance and flushing, they can last over a decade.


How to do State Select water heater thermocouple replacement? You should have a clear idea of doing that by now. No matter which gas valve you have, this guide should be enough for you as it’s a fairly easy process.

Remember to inspect the thermocouple with a multimeter to make sure that something is really wrong with it before you replace it. We also have a guide on how to reset state select water heater. Check it out when you need to reset your water heater.

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